The present invention relates to a method for automatic scheduling of a production plan, and more particularly, to a method for reducing setup change frequency of testing machines in testing factories.
The modern factories"" production lines should always fit the ever-changing customer needs and produce versatile, diversified products. In order to keep the productivity and increased throughput; production control is a major concern in large scaled factories all over the world.
It is a trend for modern factories to use an information system for production control wherein measured data from many facilities is controlled, stored, and, if necessary, processed in a central database. Thus it is also possible to retrieve individual products"" production figures or entire product ranges, complied statistics, calculated costs, determine yields, and the like. Access of these databases takes place via a personal computer, with which nearly every work place is equipped with and they are interconnected via a network for data exchange.
A semiconductor integrated circuit (IC) production factory use hundreds of process steps to manufacture desired IC devices. There is also a plurality of testing procedures to ensure the quality and reliability after versatile products are produced. In the past, the planner would collect all the information, such as work in process (WIP) data, loading density of equipment, tester status, master production schedule, etc., to manually decide how and when to make a test of each testing lot. Nevertheless, the top issue that will affect the delivery date and throughput of miscellaneous products under the fixed equipment is every testing machine""s setup change frequency. When the testing machine encounters different products after previous lots are completed, the operator will change the accessories for the following different lots in order to fit the testing requirement. In other words, the term xe2x80x9csetupxe2x80x9d is the activity to interchange the necessary accessories for the various products and verify the completeness of the change.
Changing the setup will sometimes take more than one hour in testing factories. This is because time will be wasted not only on changing the accessories, but verifying the system will also waste time. Sometimes verifying the system takes even more time. When a variety of products are developed, testing machine""s setup frequency is increased. Besides, the miscellaneous product mix will also increase the processing time of manual work and inevitably cause some faulty arrangement; this will increase setup frequency at the same time. The more frequently the tester setup changes, the less efficient the tester is utilized.
As previously described about the setup change, the arrangement of the queuing lots to the testing machine depend on the experience and even the intuition of the planner in the past. Sometimes unexpected situations such as unstable output from previous manufacturing will also confused the planner. Manually collected data from external and internal departments, and production plan""s scheduling and re-scheduling will take a lot of time. Some basic data such as processing time and tester status can only be accessed by inquiry or human memory. All these disadvantages described not only relate to the production cost, but also affect the throughput of the testing factories.
Since there are not any systematic methods in testing factories to analyze all this related information of the production plan and make an efficient use, a need is created to disclose a method for automatic production plan scheduling.
Since manual testing lot arrangements in suitable tester groups will waste a lot of time and cause a setup change increase, this invention discloses a method for automatic production plan scheduling, especially for setup change reduction.
It is an objective of this invention to provide a systematic way to manage production schedule automatically.
It is another objective of this invention to shorten planners operation time and to avoid manual mistakes.
It is a further objective of this invention to make sure each machine can produce the right lots at the right time.
First, the invention uses a more direct calculation to decide how to arrange the first priority and second priority lots to the test line according to the emergent level of the lots. Thereafter, most of the queuing lots left belong to the normal lots and need to be handled with more effort. Firstly, all testing machines and accessories should be checked to see if there is a suitable machine that can perform the test or any testing machine that fits the requirement of delivery and create warning reports if there is no machine that can fit the requirement. Next, check that whether or not the setup change is necessary. Select the machine that can provide first and doesn""t need to be setup, or select the only machine that needs to be setup. If there is more than one machine available that needs to be setup, use the reduced setup method to lower the setup frequency.
The reduced setup key is to select the idle machine to balance the output of every machine, or select the machine which has the minimum impact for the subsequent testing lots, that is, get the most efficient machine used.